CN103868855B - Based on Double-optical path single-sensor gas infrared detection system and the method for optical path-deflecting - Google Patents

Abstract

The dual-optical path single-sensor gas infrared detection system and method based on optical path deflection includes an infrared light source, a reference gas chamber, a detection gas chamber, a deflection mirror, an infrared photodetector and a deflection device. The deflection device drives the light source or a piece of reflector to deflect, so that the optical path switches between the reference gas chamber and the detection gas chamber, and reaches the infrared detector in time division. The infrared detector compares the intensity of the light signal detected twice before and after, and The common logarithm of the ratio of the two is used as the detection signal, and then converted into gas concentration by polynomial fitting according to the calibration sample. Since the present invention uses an infrared sensor, the present invention can eliminate the influence caused by the characteristic drift of the sensor in addition to helping to eliminate the influence caused by the drift of the light source.

Description

Dual optical path single sensor gas infrared detection system and method based on optical path deflection

technical field

The invention belongs to the field of spectrum online analysis of gas composition and concentration, and in particular relates to a gas infrared detection system and method based on optical path deflection with two optical paths and one sensor.

Background technique

Infrared spectroscopy can realize the quantitative analysis of almost all polar gases, and neither consumes any materials nor produces any waste during the working process, but also can work for a long time and has low maintenance costs, so it is an important method for online gas analysis. method. For some specific occasions, there are few gas components that need to be detected. For example, in some denitrification applications, it is only necessary to detect NO, and carbon emission detection only needs to detect CO ₂ . The direct use of spectrometer for analysis has high accuracy, but the cost is too high. In this case, monochromatic light or narrow-band light is often used to detect a certain gas online. Because it can eliminate the characteristic drift of the light source and the influence of environmental parameters, the dual optical path method is an important method for infrared detection of polar molecular gases. Especially in recent years, with the development of laser technology, the wavelength of infrared laser can be within a certain range. Adjustable, and can be locked at a certain wavelength, making the gas detection selectivity very high. The conventional dual optical path method uses two infrared detectors (or two detection units on one detector) to detect the reference optical path and the detection optical path respectively, as shown in Figure 1, the existing dual optical path method uses two infrared detectors The light emitted by an infrared light source 1 is reflected by the parabolic reflector 2, enters the light cutter 4 driven by the synchronous motor 3, and then enters the reference gas chamber 6 through the filter gas chamber 5, and is filled with nitrogen in the reference gas chamber 6; The light emitted by another infrared light source 1 is reflected by the parabolic reflector 2, enters the optical slice 4 driven by the synchronous motor 3, and then enters the detection gas chamber 7 through the filter gas chamber 5, and the gas to be analyzed is in the detection gas chamber 7 ; The light passing through the reference gas chamber 6 and the light passing through the detection gas chamber 7 respectively pass through the corresponding infrared detector 8, and then the gas detection is completed through the amplifier. Due to long-term use, the characteristics of the two infrared detectors will also drift to a certain extent, and the drift of the two infrared detectors is often difficult to keep consistent, which brings deviations to the gas detection results.

Contents of the invention

Aiming at the problems in the prior art, the present invention provides a dual optical path single sensor gas infrared detection system and method based on optical path deflection, which helps to eliminate the influence of environmental changes and light source drift on the gas analysis results, and can also eliminate the The impact of the characteristic drift of the infrared detector.

To achieve the above object, the present invention adopts the following technical solutions:

The dual optical path single sensor gas infrared detection system based on optical path deflection includes an infrared light source, a reference gas chamber, a detection gas chamber, a deflection mirror and an infrared detector. The light emitted by the infrared light source is reflected by the deflection mirror and enters the reference gas chamber. When the mirror or infrared light source is deflected, the light emitted by the infrared light source is reflected by the deflection mirror and enters the detection gas chamber. The circuit is connected with the microprocessor.

A reference light path fixed reflector is arranged between the deflection reflector and the reference gas chamber, and a detection light path fixed reflector is arranged between the deflection reflector and the detection gas chamber.

The deflection of the infrared light source or the deflection mirror is realized by a deflection device.

The deflection device is a stepper motor or a slider crank mechanism.

The deflection frequency range of the deflection mirror or the infrared light source is 0.1-100 Hz, and the deflection angle range is [-30°, 30°].

The infrared light source is a fixed-wavelength infrared laser, a wavelength-tunable laser, or narrow-band infrared light obtained after broadband infrared light passes through a filter.

The reference gas chamber and the detection gas chamber are two completely identical structures and materials.

The infrared detector is a photon detector based on the photoelectric effect or a heat detector based on the thermal effect; the microprocessor is a single-chip microcomputer or a digital processor.

The detection method of the double optical path single sensor gas infrared system based on optical path deflection, the light emitted by the infrared light source is reflected by the deflecting mirror and enters the reference optical path fixed mirror, and is reflected by the reference optical path fixed mirror and enters the reference gas chamber. When the mirror deflects, the light emitted by the infrared light source is reflected by the deflection mirror and enters the fixed mirror of the detection optical path, and then reflected by the fixed mirror of the detection optical path and enters the detection gas chamber. The reference gas chamber is filled with nitrogen gas, and the gas in the detection gas chamber is in a flow state. state, it enters from the air inlet of the detection gas chamber and discharges from the gas outlet; through the deflection mirror or infrared light source, the optical path is switched between the reference gas chamber and the detection gas chamber, and reaches the infrared detector in time, and the infrared detector real-time Detect the optical signal, and adjust the optical signal into an electrical signal through the conditioning circuit, and then collect it by the microprocessor. The microprocessor compares the peak values of the two detected optical signals before and after, and uses the common logarithm of the ratio As a detection signal, the result of performing quadratic or cubic polynomial calculation on the detection signal is used as the gas concentration detection result to complete the gas detection.

The specific process of performing quadratic or cubic polynomial operations is as follows: when the infrared light passes through the reference gas chamber, the peak value of the signal detected by the infrared detector is p ₁ , and when the infrared light passes through the detection gas chamber, the peak value of the signal detected by the infrared detector is p ₂ , and p ₁ and p ₂ are two adjacent signal peaks detected by the infrared detector, then the signal detected by the dual optical path gas infrared detection system is taken as s=log(p ₁ /p ₂ ), where log( ) is a common logarithmic operator, c=ls ³ +ms ² +ns is the detection result of the gas detection system, where l, m and n are the constants of the experimental calibration, c is the gas concentration result, if l is 0 , then it is a quadratic polynomial calibration, otherwise it is a cubic polynomial calibration;

The determination method of l, m and n is as follows:

1) More than three groups of standard gases are given as samples, and the respective concentrations of the samples are all over the detection range;

2) Inject the standard gas into the detection gas chamber respectively. After the detection signal is stable, the values of the measured signal s are respectively S=[s ₁ ,s ₂ ,s ₃ ,…], s ₁ ,s ₂ ,s ₃ ,...are the mean values of more than 10 consecutive measurement results, and their corresponding gas concentration values are C=[c ₁ ,c ₂ ,c ₃ ,...];

3) Carry out polynomial approximation by partial least squares method, obtain parameter P=[l, m, n];

P=inv(SAS ^T )SAC ^T

In the formula, A is a square matrix with non-zero parameters only on the main diagonal, its dimension is the same as the number of samples, and it satisfies the relationship A ₁₁ ≤A ₂₂ ≤A ₃₃ ≤..., A ₁₁ , A ₂ 2, A ₃₃ , ... are weighting coefficients set by the user.

Compared with the prior art, the present invention has beneficial effects: in the present invention, the light source or the deflection mirror deflects back and forth, so that the infrared light emitted by the light source is deflected back and forth, so that the optical path is switched between the reference gas chamber and the detection gas chamber, and the split When it reaches the infrared detector, the signal detected by the infrared detector is conditioned and transmitted to the microprocessor system, which can realize the gas detection. The invention has simple structure and accurate measurement results. Because the present invention uses an infrared detector, this method can eliminate the influence caused by the characteristic drift of the infrared detector in addition to the influence of the drift of the light source and the environment change, such as temperature. Influence, save the light modulation system of the infrared detector in the conventional gas infrared detection device.

Description of drawings

Figure 1 is a structural diagram of a conventional dual optical path gas infrared detection system;

Figure 2 is an optical path diagram of a single-sensor dual-optical-path gas detection device based on optical deflection deflected by a mirror;

Figure 3 is a schematic cross-sectional view of the reference air chamber;

Fig. 4 is an optical path diagram of a single-sensor dual-optical-path gas detection device based on light deflection and light source deflection.

Among them, 1-infrared light source; 2-parabolic reflector; 3-synchronous motor; 4-light cutter; 5-filter air chamber; 6-reference air chamber; -amplifier; 10-deflection mirror; 11-reference optical path fixed mirror; 12-detection optical path fixed mirror; 13-window; 14-window fastener; 15-air chamber cavity; 16-air inlet ; 17 - air outlet.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 2, a single-sensor dual-optical path gas detection system based on optical deflection includes an infrared light source 1, a deflection mirror 10, a reference optical path fixed mirror 11, a detection optical path fixed mirror 12, a reference gas chamber 6, a filter Gas chamber 5, deflection device, detection gas chamber 7, an infrared detector 8 and its conditioning circuit, and microprocessor. The light emitted by the infrared light source 1 is reflected by the deflecting reflector 10 and then enters the reference gas chamber 6 through the reference light path fixed reflector 11. When the deflecting reflector 10 or the infrared light source 1 is deflected, the light emitted by the infrared light source 1 passes through the deflecting reflector 10 reflection and then enter the detection gas chamber 7 through the fixed mirror 12 of the detection optical path. connected.

Infrared light source 1 can be a fixed-wavelength infrared laser, a wavelength-tunable laser, or a narrow-band infrared light obtained after broadband infrared light passes through a filter, as long as the infrared light emitted by it contains the wavelength of the absorption line of the gas to be detected. Yes, for example, if the detected gas is CO ₂ , the infrared spectrum emitted by the light source includes light with a wavelength of 2.7 μm, and if the detected gas is NO ₂ , the infrared spectrum emitted by the light source includes light with a wavelength of 540 nm That's it.

The reference gas chamber 6 and the detection gas chamber 7 are two gas chambers with identical structures and materials. The cross-sectional schematic diagram of the reference gas chamber 6 is shown in Figure 3. The gas chamber cavity 15 of the reference gas chamber 6 is filled with nitrogen, and the gas outlet 16 and the air inlet 17 are sealed, and the window 13 is fixed at both ends of the reference gas chamber 6 by the window fastener 14, while the gas in the detection chamber 7 is in a flowing state and enters from the air inlet of the gas chamber. Exit from the air outlet.

The deflection of the deflection mirror 10 or the infrared light source 1 is realized by a deflection device, which may be a stepping motor or a slider crank mechanism. The light emitted by the infrared light source 1 is directly irradiated on the deflection mirror 10, and the deflection device drives the deflection mirror 10 to swing back and forth, so that the infrared light is alternately irradiated on the reference optical path fixed reflector 11 and the detection optical path fixed reflector 12. The reflector makes the light reach the infrared detector 8 after passing through the reference gas chamber 6 and the detection gas chamber 7 respectively.

The infrared detector can be a photon detector based on the photoelectric effect, or a thermal detector based on the thermal effect, such as a thermal bolometer, a thermopile and a pyroelectric element. The deflection frequency range is 0.1-100Hz, and the angle range is -30°-30°. The deflection frequency range used depends on the performance index of the selected infrared detector. For example, the scanning period of the AGM22 gas detection infrared detector can be selected as: 0.5s, 5s, 10s, 20s. The infrared detector detects the light signal in real time, and the conditioning circuit and the subsequent signal micro-processing system record the detection results. The microprocessor system can be a single-chip microcomputer or a digital processor. The conditioning circuit is mainly to amplify and filter the detector signal. The amplification factor is determined by the analog-to-digital converter (A/D) of the selected microprocessor system. . For example, the A/D input signal range of the 51 single-chip microcomputer is 0-5V, so the amplification factor should be set to the value when the maximum output voltage is about 4.8V when the light is irradiated on the detector through the reference gas chamber. The filter is used to filter out noise, and its passband cut-off frequency corresponds to the scanning frequency; the microprocessor system is used to record the test signal and convert it into gas concentration.

The detection method of the double optical path single sensor gas infrared system based on optical path deflection, the light emitted by the infrared light source 1 is reflected by the deflecting reflector 10 and enters the reference optical path fixed reflector 11, and is reflected by the reference optical path fixed reflector 11 and enters the reference gas chamber 6, when When the infrared light source 1 or the deflection mirror 10 is deflected, the light emitted by the infrared light source 1 is reflected by the deflection mirror 10 and enters the detection optical path fixed reflection mirror 12, and is reflected by the detection optical path fixed reflection mirror 12 and enters the detection gas chamber 7, referring to the gas chamber 6 Nitrogen is filled in the middle, the gas in the detection gas chamber 7 is in a flowing state, enters from the air inlet 16 of the detection gas chamber 7, and is discharged from the gas outlet 17; 6 and the detection gas chamber 7 are switched to reach the infrared detector 8 in time-sharing, the infrared detector 8 detects the optical signal in real time, and adjusts the optical signal into an electrical signal through the conditioning circuit, which is then collected by the microprocessor, and the microprocessor passes Compare the peak values of the light signals detected twice before and after, and use the common logarithm of the ratio of the two as the detection signal, and use the result of the second or third polynomial operation on the detection signal as the gas concentration detection result. When the light passes through the reference gas chamber 6, the peak value of the signal detected by the infrared detector 8 is p ₁ , and when the infrared light passes through the detection gas chamber 7, the peak value of the signal detected by the infrared detector 8 is p ₂ , and p ₁ and p ₂ are infrared detection If the peak value of the signal is detected twice adjacently by the detector, the signal detected by the dual optical path gas infrared detection device is taken as s=log(p ₁ /p ₂ ), where log(·) is commonly used as a logarithmic operator, c= ls ³ +ms ² +ns is the detection result of the gas detection system, where l, m and n are the constants of the experimental calibration, c is the result of the gas concentration, if l is 0, it is the quadratic polynomial calibration, otherwise it is the cubic polynomial calibration .

The determination method of l, m and n is as follows:

1) More than three groups of standard gases are given as samples, and the concentration of each sample is throughout its detection range. For example, assume that the detection device is used to monitor CO ₂ , and its concentration range is 0-20% by volume, and the selected concentrations of 20%, 5%, 1% CO ₂ and nitrogen are used as standard gases, that is, the concentration vector is C=[20,5,1,0];

2) Inject the standard gas into the detection gas chamber of the system respectively. After the detection signal is stable, the values of the signal s are respectively measured as S=[s ₁ , s ₂ , s ₃ ,…], s ₁ , s ₂ , s ₃ ,… are the mean values of more than 10 consecutive measurement results, and their corresponding gas concentration values are C=[c ₁ ,c ₂ ,c ₃ ,…];

3) The partial least square method is used for polynomial approximation, and the parameter P=[l,m,n] is obtained.

P=inv(SAS ^T )SAC ^T

In the formula, A is a square matrix with non-zero parameters only on the main diagonal, its dimension is the same as the number of samples, and it satisfies the relationship A ₁₁ ≤A ₂₂ ≤A ₃₃ ≤..., A ₁₁ , A ₂₂ , A ₃₃ , ...is a weighting coefficient set by the user.

In the present invention, the deflection of the deflection mirror can also be replaced by the deflection of the light source, as shown in FIG. 4 . The deflection device drives the light source to deflect back and forth. The infrared light generated by the light source is irradiated on the deflection mirror and reflected on the reference optical path fixed mirror 11, and then reaches the infrared photodetector through the reference gas chamber 6, or is reflected by the deflection mirror 10 to the fixed detection optical path. on the mirror 12, and then through the detection gas chamber 7 to reach the infrared photodetector.

The present invention aims at the influence brought by the consistent drift of the characteristics of the double-infrared detectors in the process of double-infrared detectors and double-optical-path gas infrared online analysis. A deflection device is used to drive the light source or a piece of reflector to deflect back and forth, so that the infrared light emitted by the light source is deflected back and forth, thereby The optical path is switched between the reference gas chamber and the detection gas chamber, and reaches the infrared detector in time division. After the signal detected by the infrared detector is conditioned, it is transmitted to the microprocessor system. The system compares the light detected twice before and after. The intensity of the signal, and the common logarithm of the ratio of the two as the gas detection signal of the gas detection device, and then convert it into a gas concentration according to the polynomial obtained from the calibration sample. Because what adopts in the present invention is an infrared detector, therefore, this method can not only help to eliminate the influence that environment change, light source drift brings to the gas analysis result, but also can eliminate the characteristic drift brought by the infrared detector. influences.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments. It cannot be determined that the specific embodiments of the present invention are limited thereto. Under the circumstances, some simple deduction or replacement can also be made, all of which should be regarded as belonging to the scope of patent protection determined by the submitted claims of the present invention.

Claims (8)

1. based on the Double-optical path single-sensor gas infrared detection system of optical path-deflecting, it is characterized in that, comprise infrared light supply (1), reference gas chamber (6), detect air chamber (7), deflection mirror (10) and an infrared eye (8), the light that infrared light supply (1) sends enters reference gas chamber (6) through deflection mirror (10) reflection, when making deflection mirror (10) or infrared light supply (1) deflects, the light that infrared light supply (1) sends enters through deflection mirror (10) reflection and detects air chamber (7), light path is at reference gas chamber (6) and detect switching between air chamber (7), timesharing arrives infrared eye (8), infrared eye (8) is connected with microprocessor through modulate circuit,

Be provided with reference path stationary mirror (11) between described deflection mirror (10) and reference gas chamber (6), be provided with between deflection mirror (10) and detection air chamber (7) and detect light path stationary mirror (12);

Described infrared light supply (1) or deflection mirror (10) are deflected and to be realized by inflector assembly.

2. the Double-optical path single-sensor gas infrared detection system based on optical path-deflecting according to claim 1, it is characterized in that, described inflector assembly is stepper motor or slider-crank mechanism.

3. the Double-optical path single-sensor gas infrared detection system based on optical path-deflecting according to claim 1 and 2, it is characterized in that, the frequency range that described deflection mirror (10) or infrared light supply (1) deflect is 0.1-100Hz, range of deflection angles is [-30 °, 30 °].

4. according to the Double-optical path single-sensor gas infrared detection system based on optical path-deflecting described in claim 3, it is characterized in that, described infrared light supply is fixed wave length infrared laser, Wavelength tunable laser or the arrowband infrared light of broadband infrared light by obtaining after optical filter.

5. according to the Double-optical path single-sensor gas infrared detection system based on optical path-deflecting in claim 1 or 4 described in any one, it is characterized in that, described reference gas chamber (6) and detection air chamber (7) are two identical air chambers of structure and material.

6. according to the Double-optical path single-sensor gas infrared detection system based on optical path-deflecting described in claim 1, it is characterized in that, described infrared eye (8) is based on photoelectric photon detector or the thermal detector based on thermal effect; Microprocessor is single-chip microcomputer or digital processing unit.

7. the detection method of the Double-optical path single-sensor gas infrared system based on optical path-deflecting according to claim 6, it is characterized in that, the light that infrared light supply (1) sends enters reference path stationary mirror (11) through deflection mirror (10) reflection, reference gas chamber (6) is entered through reference path stationary mirror (11) reflection, when infrared light supply (1) or deflection mirror (10) deflect, the light that infrared light supply (1) sends enters through deflection mirror (10) reflection and detects light path stationary mirror (12), light path stationary mirror (12) reflection enters and detects air chamber (7) after testing, inflated with nitrogen in reference gas chamber (6), the gas detected in air chamber (7) is then in flow state and enters from the air intake opening (16) detecting air chamber (7), discharge from gas outlet (17), by deflection mirror (10) or infrared light supply (1), make light path at reference gas chamber (6) and detect switching between air chamber (7), timesharing arrives infrared eye (8), infrared eye (8) real-time detection light signal, and by modulate circuit, light signal is nursed one's health into electric signal, again by microcontroller acquires, the peak value of light signal of microprocessor by detecting for twice before and after comparison, and using the common logarithm of both ratio as detection signal, and the result of this detection signal being carried out to secondary or cubic polynomial computing is as gas concentration testing result, complete the detection of gas.

8. the detection method of the Double-optical path single-sensor gas infrared system based on optical path-deflecting according to claim 7, it is characterized in that, described in carry out secondary or cubic polynomial computing detailed process be: the signal peak setting infrared light to detect by reference to infrared eye (8) time air chamber (6) is as p ₁, the signal peak that infrared light is detected by infrared eye (8) during detection air chamber (7) is p ₂, and p ₁and p ₂be the adjacent signal peak detected for twice of infrared eye, then this signal detected by double light path gas infrared detection system is taken as s=log (p ₁/ p ₂), wherein log () is common logarithm operator, c=ls ³+ ms ²+ ns is the testing result of gas detecting system, and wherein l, m and n are the constant of experimental calibration, and c is gas concentration result, if l is 0, then for quadratic polynomial is demarcated, otherwise is cubic polynomial demarcation;

The defining method of l, m and n is as follows:

1) calibrating gas of given more than three groups is as sample, and sample concentration is separately throughout its sensing range;

2) be injected into respectively by calibrating gas in detection air chamber, after signal stabilization to be detected, the value recording signal s is respectively respectively S=[s ₁, s ₂, s ₃... ], wherein, s ₁, s ₂, s ₃... be the average of the measurement result of continuous more than 10 times, the gas concentration value of their correspondences is respectively C=[c ₁, c ₂, c ₃... ];

3) adopt partial least square method to carry out approximation by polynomi-als, ask for parameter P=[l, m, n];

P＝inv(SAS ^T)SAC ^T

In formula, A only has parameter on principal diagonal to be the square formation of non-zero, and its dimension is identical with sample size, and meets relation A ₁₁≤ A ₂₂≤ A ₃₃≤ ..., A ₁₁, A ₂₂, A ₃₃... it is the weighting coefficient be set by the user.